Sweetening process



Patented Sept. 22, 1936 UNITED STATES SWEETENINGI r'aocEss" f Arnold Belchetz, Houston, Tex.,- assignor to Shell.

Development Company, San Francisco, Calif., a. corporation of Delaware V No Drawing. Application April 6, 1935, Serial No. 15,091' t 4 Claims. (01. 196-33.)

This process pertains to the treatment of liquid solutions containing sulfur compounds known as thio-alcohols or mercaptans, and is more particularly concerned with a method of refining hydrocarbon or other organic mixtures containing such compounds.

' lthough various methods, such as oxidation, scrubbing 'withconcentrated caustic soda, etc.,

a have been developed to remove these compounds,

by far the most widely used process for this purpose is the doctor treatment, which consists in agitating a sour, or mercaptan-containing hydrocarbon. mixture; with an aqueous alkaline solution of sodium plumbite and a small quantity isobtained by treatment with relatively small amounts of sodium plumbite. This process may beapplied for sweetening any liquid solution contalning mercaptans, such as straight run or pressure distillates and other hydrocarbon oils either natural or synthetic, like products of hydrogenation and/ or polymerization as well as non-hydrocarbon solutions, like synthetic alcohols or ketones, and in general any solutions containing mercaptans. The process is particularly suitable for sweetening neutralized acid treated cracked distillates.

I have discovered that in order to sweeten a sour solution it is not necessary to have all the mercaptans converted to lead mercaptides as a preliminary step. I have found that under certain conditions it is possible to effect the oxidation of mercaptans (i. e. sweetening) by means of free sulfur, in the presence of lead mercaptides. Under these conditions lead mercaptides appear to act as catalysts in promoting the sweetening reaction between mercaptans and the oxidizing agent. I have found that this sweetening reaction proceeds apparently simultaneously with a relatively slow decomposition of lead mercaptides, so that at the end, if a sufficient quantity of the oxidizing agent was used, both the mercaptans and mercaptides are decomposed and the originally sour solution is sweetened at the expense of free sulfur and sodium plumbite which areconverted into P108 and NaOH. It is evident that by practising my process a great economy and saving of valuable litharge and alkali is effected. v I

Briefly stated, my'process consists in treating with an alkaline plumbite only a relatively small quantity'of a sour solutionf'thereby converting the mercaptans into lead mercaptides, and thor oughly blending said treated solution with another quantity of a solution containing free mercaptans and free'sulfur. The resulting mixture becomes sweet and lead'sulfide formed from the decomposition of mercaptides separates out and can be removed from the treated liquid by settling, filtering or centrifuging. By blending is meant the step of combining two liquids to form a solution; often it is desirable to accompany this step of bringing two liquids together by vigorous agitation to effect homogeneity and to promote chemical interactionof dissolved reagents. V j

For example, a portionjof a sour distillate from a Persian crude having a free sulfur content of theorder of 0.005% was treated with an" excess of an aqueous sodium plumbite solution suitable for doctor treatment and the hydrocarbon solution of lead mercaptides thus obtained was blended with varying proportions of the untreated portion of the same sour distillate. The following results were obtained from the blends made:

Blend Sodium plumbit Untreated Doctor test treated distillate,

distillate in volumes involumes 1 1 Negative. 1 3 Do. 1 4 tly positive. 1 5 Positive.

treatment, it is essential for the successful-operation of the new process to have sumcient amounts of free sulfur present in the mixture containing both mercaptans and mercaptides. It is preferable to have free sulfurpresnt in" the combined solutions inathe amount which.,is ,1;

approximately equivalent to the amount of mercaptans, i. e., one mol of sulfur for two mols of mercaptans, although smaller or greater amount s of sulfur may be used. This sulfur may be hat-1 urally present in one or both solutions undergoing the treatment, or it may be added theretobefore, during or after the two solutions are combined, However, when theina'tur'ally present amounts of free sulfur are insuflic'ient to "com-v plete the sweetening, I prefer' to add small amounts of free'sulfurto jthe second solution, which was not treated with alkaline'plumbite, and which is subsequently blended with the plumbite treated solution to efiectthe sweeten ing. Sulfunmay be dissolved ldirectl'y in the'distillateto be treated, or introduced in the" form of, a solution in vasuit'alole solvent. The complee tion of the sweetening reaction'in the presence of suflicientor excessive amounts of 'freefsulfur isindicated by'the precipitationfof PbS. How'- Vever, in some. 'cases even when stoichiometric amounts of free sulfur, mercaptides and mercaptans are brought 'tog'ether, the precipitation of lead sulfide does not take'place readily;'in such cases I prefer to combine. the process of my invention with that described in thejlSnyder Patent No. 1,985,955,i. el',,to complete the refining process 'by treating the solution whose color be,- came'brownish as the result of combining of mercapta'ns and mercaptides, with clay.

' e;di la s r ed by. h metho at least equal; andin many cases superior to "those refined by a complete treatment with sodium plumbite with regard to the doctor test, corrosive sulfur test and color"stability, j 'Ifhey are decidedly superior in so far as odor isconcerned, since the harsh odor which is characteristic of distillates refined by a complete sodium plumbite treatment is entirely absent in products sweetened by this method.

I claim as my invention:

1. In the process of treating a solution of mercaptans in an organic solvent to convert mercaptans to disulfides, the steps of dividing said solution into two portions, treating one portion with an alkaline plumbite reagent under conditionsto convert mercaptans to mercaptides soluble in said solvent and blending the resultant solution of mercaptides with the untreated portion containing mercaptans in the presence of sulfur and in the absence of lead-containing reagents other Ji lian lead mercaptides, thereby converting mercaptans and mercaptides in the resuiting mixture to disulfides.

In the process of treating a solution of merjc'aptans in an organic solvent to convert mercaptans to disulfides, the steps of dividing said solution into two portions in a ratio at least 1:3, treating the smaller portion with an alkaline plumbite reagent under conditions to convert mercaptans to mercaptides, separating the treated portion containing mercaptides from the reagent-and blending the saidtreated portion with the untreated portion containing mercaptans in the presence of free sulfur, thereby converting' mercaptans and mercaptides contained in the resulting mixture to disulfides.

3. In the process of sweetening a hydrocarbon oil containing mercaptans, the improvement cQmprising treatingsaid oil; with sodium plumbite reagent'un'derconditions to convert mercaptans tof'lead mercaptides, thereby forming a solution of lead mercaptides in the treated oil, separating said solution of mercaptides from the reagent and blending said solution with a hydrocarbon oil containing mercaptans in the presence of a sufiicient amount of sulfur to convert the ni'ercaptans andmercaptides in the resulting mixture to disulfides.

4. In the process of sweeting a sour hydrocarbon oil containing mercaptans, the step of mixing said oil with a solution consisting essentially of a hydrocarbon oil and lead mercaptides in the presence of an amount of sulfur sufiicient to convert the mercaptans and mercaptides in the resulting mixture to disulfides, and in the absence of lead-containing reagents other than lead mercaptides.

' ARNOLD BELCHETZ. 

